As people increasingly value holiday celebrations, many manufacturers have started to provide household decorations matching the holiday spirits. Taking a Christmas light for instance, FIG. 1 shows a sectional view of such conventional Christmas light. A common Christmas light is usually formed by two parallel conductive lines 6 and a plurality of light emitting elements connected across these two conductive lines 6. The flexibility of the two conductive lines 6 enables the Christmas light to be installed at various places according to actual requirements. The conventional Christmas light is likely deployed outdoors. To prevent the two conductive lines 6 from humidity that may cause a failure in conducting electricity, manufacturers of Christmas lights frequently dispose an insulating layer 61 at an outer periphery of each of the two conductive lines 6, so as to prevent humidity from entering the conductive lines 6. However, with the popularity of light emitting diodes (LED) 7, there are also manufacturers that apply the LED 7 on Christmas lights. When the LED 7 is powered on, a waste heat 71 of the LED 7 is accumulated at a rear portion of the LED 7 and further enters the two conductive lines 6. As the surfaces of the two conductive lines 6 are covered by the insulating layer 61, the waste heat 71 is confined at the two conductive lines 6. When the Christmas light is lighted for an extensive period of time, the excessively accumulated waste heat 71 causes the two conductive lines 6 to rise in temperature, and heats and melts the insulating layer 61 to reveal the two conductive lines 6. As a result, the Christmas light may still malfunction due to the two conductive lines 6 being affected by humidity to even lead to an accident of short circuitry and electrical fire.